Carpeting stairs: full-width carpet or a runner, and how much

Measure a step

A step is a tread, the flat part you stand on, and a riser, the vertical part. Carpet covers both and wraps around the front edge of the tread, called the nosing. So each step needs the tread depth, plus the riser height, plus a little more to go round the nosing.

Measure the tread from the riser to the front of the nosing, and the riser from tread to tread. Count the risers, not the treads: a flight usually has one more riser than tread, because the top riser leads to the upper floor. A typical US flight between storeys has 13 to 15 risers.

A flight worked through

From a roll

A 39 inch wide piece is cut from a 12 ft roll, so three pieces fit across the roll. An installer cuts a staircase in strips across the roll, often two or three steps per piece, with the pile running down the stairs. The yardage quoted for stairs is often higher than the arithmetic, because of the cuts; ask how it was worked out. Most carpet stores price stairs per step for the installation, on top of the carpet.

A runner

A runner covers the middle of the stair and leaves a strip of wood or paint showing on each side. It is sold by the linear foot, typically 27 inches wide, leaving 3 to 5 inches of tread at each side on a 36 inch stair.

The stair carpet calculator handles both full width and runners, with landings, pad and pattern repeat. A patterned runner must start each step at the same point of the pattern, which adds up to one repeat per step if the repeat does not divide evenly into the step.

Waterfall or Hollywood

There are two ways to fit carpet on a step. Waterfall lets the carpet fall straight from the nosing to the next tread, leaving a small gap behind it at the riser. It is quicker and uses slightly less carpet. Hollywood, also called cap and band, wraps the carpet tightly under the nosing and down the riser, following the shape of the step. It looks tailored and uses a little more carpet. The 1.5 inch allowance for the nosing covers either.

Landings and winders

A landing is counted like a small room: its area, with the pile running the same way as the stairs. A 3 × 3 ft landing adds 9 sq ft, 1 sq yd. Winders, the triangular steps that turn a corner, are measured at their widest and cut as rectangles; they waste more carpet than straight steps. An open-sided stair needs the carpet finished at the open edge, by binding or by turning it under, which the tuck allowance covers.

Pad on stairs

Stair pad must be firm: at least 8 lb density and no thicker than 7/16 inch. A soft pad makes the carpet roll over the nosing and wear through. The pad covers the tread and wraps the nosing, stapled under the nosing and at the back of the tread; it does not go on the riser. The carpet padding calculator counts pad by the area, and the carpet padding guide explains density.

Tack strip on stairs

On each step, a short length of tack strip is nailed to the tread at the back, close to the riser, and another to the riser near the bottom. That is two pieces per step, about the stair width each. The tack strip calculator counts the room perimeter; for stairs add two times the width per step.

Not carpet? Hard stair treads

If the stairs are to be wood, laminate or vinyl instead, they need stair nosings and treads, counted by the step with a different calculation. The stair flooring calculator counts treads, risers and nosings. The carpet roll guide covers the floors at the top and bottom of the stairs, and the rug size guide covers a rug for the hall at the bottom.

Safety

The International Residential Code limits risers to 7 3/4 inches and asks for treads at least 10 inches deep. A thick carpet and pad make the tread effectively shallower and soften the nosing, which makes stairs harder to read underfoot. Choose a low, dense carpet for stairs, fit it tightly, and keep the nosing crisp.